1. Study Plan for Lizzi Scholarship in 2004
IWM2004: August 25th, 2004
Shingo MORIMASA
Graduate Student, GeoMechanics Group,
Toyohashi University of Technology
(Before Presentation)
Thank you.
I'm very honored to be here as a Lizzi scholorship student.
I’ll make good use of these references for my study.
I'll do my best to live up to your expectations.
Thank you Mr. chairman.
I am Shingo MORIMASA, a graduate student of Toyohashi University of Technology, Japan.
Then I'd like to talk about my study plan for Lizzi Scholorship in 2004.

2. Contents of my presentation
Title and aim of my study
Previous study
Network effect
Prestressed micropile method
Study plan
Simulation method of the load bearing behavior
Effects of network and prestress
In this presentation, first I'm going to talk about the title and the aim of my study.
Then I’m going to review some of the early studies mentioning briefly network effect, prestressed method and so on, and their technical issues.
Finally, I am going to talk about my future plans.

3. Title and the aim of my study
Title:　An analytical study on the bearing capacity of the foundation reinforced with prestressed micropiles
Aim: Analytic clarification of the mechanism of the mobilization of load bearing capacity of foundation reinforced with prestressed micropiles
The title is "An analytical study on the bearing capacity of the foundation reinforced with prestressed micropiles."
This study aims to clarify analytically the mechanism of the mobilization of load bearing capacity of foundation reinforced with prestressed micropiles.

4. Previous study
Load Bearing Mechanism has been studied by Otani, Tsukada, Miura et al.
“Model Loading Tests on The Footing Reinforced with Prestressed Micropiles”
“Large-Scaled Field Loading Test on The Footing Reinforced with Prestressed Micropiles”
Laboratory model loading tests
Network effect
Effect of prestress
Filed loading tests
Verification of the prestressed micropile method
Let me refresh your memory on the early study.
Load bearing mechanism by micro pile foundation has been studied by Otani, Tsukada, Miura et al.
For the details, please read these papers, which were presented in IS-Kyushu, 2001.
In the laboratory model loading tests, network effect and effect of prestress were investigated.
And field loading tests, the prestressed micropile method were verified.
Then I’d like to mention briefly about these test results.

5. Laboratory Loading Tests
This figure shows the apparatus used in the laboratory model loading tests.
The model foundation is loaded vertically and horizontally by this apparatus
Single micropile, footing and footing reinforced with micropiles were loaded in this test.
Test apparatus

6. Network Effect Index Ine
Footing reinforced with micropile
Bearing capacity
To assess the degree of improvement of the bearing capacity with micropiles quantitatively, the network effect index ‘Ine’ was intoduced.
The value of unity in ‘Ine’ means that the load borne by the footing reinforced with micropiles is equal to the summation of loads borne by the surface footing and the micropile group.
If the confining effect by the interaction between the subsoil, footing and the micropile group is positive, the interaction improves the bearing capacity, and the value of ‘Ine’ becomes larger than unity.
They call this interaction ‘Network effect’.
Bearing capacity
Only footing
Only micropile

7. Test results for network effect
Laboratory Loading Test
Test results for network effect
Network effect
On the surface footing reinforced with micropiles, the improvement of bearing capacity due to network effect was recognized in the case of dense ground.
In the case of medium or loose ground, however, the network effect was not mobilized positively.
It can be said that the confinement of the ground material with the interaction between the footing and the micropile group plays an important role in the improvement of bearing capacity.
So we thought of inducing prestress to the micropile group before loading, in order to confine the subsoil and improve the bearing capacity.
Degree of settlement
Dense ground --- bearing capacity was improved
(Network effect was mobilized)
Medium, loose ground --- Network effect wasn’t mobilized

8. Effect of Prestress
This is the illustration of the application of prestress to micropiles.
As a reaction of the prestress, the initial base pressure and confining stress on subsoil is simultaneously increased.

9. Model footing for applying prestress
Laboratory Loading Test
Model footing for applying prestress
This is the model footing used for applying prestress.
The prestress to the micropile was about 50 percents of it’s ultimate pullout resistance in the laboratory loading tests.

10. Test results for prestress effect
Laboratory Loading Test
Test results for prestress effect
With prestress
Network effect
The red lines indicate the intensity of network effect mobilized by the footings reinforced with prestressed micropiles.
Even in the medium loose ground, network effect index ‘Ine’ was more than unity.
This figure tells that the bearing capacity was increased almost 100 percents with the prestress to micropile group equivalent to a half of ultimate bearing load of the micropile group.
Degree of settlement
Even in the medium loose ground, bearing capacity was improved due to network effect by prestress

11. Field loading tests Plan view Vertical Loading test
This is the model footings prepared for applying prestress and the loading system in the field loading tests.
In the field loading test, not only vertical loading test but also horizontal loading test was conducted.
Vertical Loading test
Horizontal Loading test
Cross section

12. The results for prestress effect
Field Loading Test
The results for prestress effect
With prestress
With prestress
Without prestress
Without prestress
Summation of
footing and
8 micropiles
These figure show the load-displacement relationship.
Also in the field loading test, network effect was mobilized and bearing capacity with prestress became higher than that without prestress.
Especially, the effect of prestress was significant in the horizontal movement control.
Vertical loading test
Horizontal loading test
Also in field loading test, network effect was mobilized.
The effect of prestress was significant in the horizontal
movement control.

13. Development of simulation method
Simulation method would be
Non-liner, 2-D or 3-D FEM　may be necessary
Appropriate constitutive model for
confining pressure dependent stress-strain behavior of ground material
Appropriated interface for
interaction between micropiles and ground material
Let me move to my future study plan.
In my study plan, the mechanism of the improvement of load bearing capacity by the prestressed micropile method is investigated by means of analytical method.
And the method for simulation of the behavior of prestressed micropile foundation is proposed.
The appropriate constitutive model for confinement effect on ground material and the mechanical model for the interaction between flexible pile such as micropile and ground material, are discussed.

14. Thanks to IWM
I am going to conduct this study hereafter, and now preparing for the study.
I’d like to present the results of the study in the IWM meetings next a few years.
I hope that the study contributes the development of the rational design of micropile foundation.
I have decided to go on to the doctoral course, so I’ll do my best to live up to your expectations.
I would like to finish my presentation with my ambition.
I am going to conduct this research hereafter and now preparing for the study.
I’d like to present the results of the study at the IWM meetings next a few years.
I hope that the results will be utilized in the design of micropile foundation.
I have decided to go on to the doctoral course, so I’ll do my best to live up to your expectations.
Thank you for your attention.

15. Thank you for your attention !
End of the Presentation